CVE Intelligence
Medium Memory corruption

CVE-2026-118370 — libexpat through 2.9.0 Integer Overflow in storeAtts via attIndex and nPrefixes

libexpat through 2.9.0 contains a signed integer overflow vulnerability in storeAtts() in lib/xmlparse.c that allows attackers to trigger out-of-bounds writes via oversized attribute counts. Attackers can supply a multi-gigabyte document with a start tag carrying over 2^30 attributes to overflow attIndex and nPrefixes, crashing applications or corrupting heap memory.

Published Oct 28, 2026 · Updated Oct 28, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: VulnCheck

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 0.4% (30-day exploitation probability)+6
  • Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
0.44%
ahead of 38% of scored CVEs · Oct 28, 2026
Affects
Libexpat
Libexpat
CVSS base
5.9
Medium · 2 source(s)

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Libexpat Libexpat).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
  4. Search available logs for exploit probes matching the vulnerability class (memory corruption), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Libexpat Libexpat ≤ 2.9.0 Vulnerable CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
8.2 CVSS 4.0 High — — disclosure@vulncheck.com via NIST National Vulnerability Database
8.2 CVSS 4.0 High — — VulnCheck via CVE Program (cve.org) e CISA ADP
5.9 CVSS 3.1 Medium 2.2 3.6 disclosure@vulncheck.com via NIST National Vulnerability Database
5.9 CVSS 3.1 Medium — — VulnCheck via CVE Program (cve.org) e CISA ADP
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H (score shown at the top: disclosure@vulncheck.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-190 · Integer Overflow or Wraparound

Other CVEs with this weakness →

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
  • Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.
web/proxy/WAF logsnetwork IDS/IPSendpoint telemetry (EDR)crash dumps

Timeline

What happened to this CVE, newest first.

  • 2026
  • Source status changed · Received → Awaiting Analysis
    Oct 28, 2026 · NIST National Vulnerability Database
  • Affected products added · libexpat/libexpat
    Oct 28, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 28, 2026
  • CVSS changed · 5.9
    Oct 28, 2026 · NIST National Vulnerability Database
  • Source status changed · → Received
    Oct 28, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 28, 2026 · Alertas do Telegram
  • CVE published
    Oct 28, 2026 · VulnCheck

Source activity

Repeated readings are counted rather than listed.

  • 1× References added · Oct 28, 2026 – Oct 28, 2026
  • 1× Official description updated · Oct 28, 2026 – Oct 28, 2026

References

6 on the record

Elsewhere on this site

Libexpat
every CVE for this vendor
Memory corruption
same class
CWE-190
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-117610 libexpat through 2.9.0 NULL Pointer Dereference via External Entity Subparser 1d
  • CVE-2026-115506 libexpat through 2.9.0 Denial of Service via Billion Laughs Detection Delay 6d
  • CVE-2026-113351 libexpat 2.7.2 through 2.9.0 Denial of Service via XML_ParserReset 9d
  • CVE-2026-77214 libexpat Heap Buffer Over-read in xmlparse.c via XML_ParseBuffer 21d
  • CVE-2026-102633 libexpat 2.7.2 through 2.8.5 Integer Overflow in expat_realloc 29d
  • CVE-2026-93990 Expat before 2.8.5 Malformed UTF-16 Acceptance via Unchecked Surrogate Sep 19, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No fixed version, patch or mitigation documented.
  • No CISA SSVC assessment.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-118370 is "libexpat through 2.9.0 Integer Overflow in storeAtts via attIndex and nPrefixes", rated Medium. It affects Libexpat (Libexpat); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.9 describes technical severity. EPSS 0.44% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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